ABSTRACT
The inducible co-stimulator (ICOS) is a member of the CD28/B7 superfamily, and delivers a positive co-stimulatory signal to activated T cells upon binding to its ligand (ICOS-L). Dysregulation of this pathway has been implicated in autoimmune diseases and cancer, and is currently under clinical investigation as an immune checkpoint blockade. Here, we describe the molecular interactions of the ICOS/ICOS-L immune complex at 3.3 Å resolution. A central FDPPPF motif and residues within the CC' loop of ICOS are responsible for the specificity of the interaction with ICOS-L, with a distinct receptor binding orientation in comparison to other family members. Furthermore, our structure and binding data reveal that the ICOS N110 N-linked glycan participates in ICOS-L binding. In addition, we report crystal structures of ICOS and ICOS-L in complex with monoclonal antibodies under clinical evaluation in immunotherapy. Strikingly, antibody paratopes closely mimic receptor-ligand binding core interactions, in addition to contacting peripheral residues to confer high binding affinities. Our results uncover key molecular interactions of an immune complex central to human adaptive immunity and have direct implications for the ongoing development of therapeutic interventions targeting immune checkpoint receptors.
Subject(s)
Antibodies/therapeutic use , Antigen-Antibody Complex/chemistry , Inducible T-Cell Co-Stimulator Ligand/chemistry , Inducible T-Cell Co-Stimulator Protein/chemistry , Molecular Mimicry/immunology , Amino Acid Sequence , Antigen-Antibody Complex/metabolism , CD28 Antigens/metabolism , Humans , Hydrophobic and Hydrophilic Interactions , Inducible T-Cell Co-Stimulator Ligand/metabolism , Inducible T-Cell Co-Stimulator Protein/metabolism , Kinetics , Ligands , Models, Molecular , Protein Binding , Protein MultimerizationSubject(s)
Inducible T-Cell Co-Stimulator Ligand/deficiency , Severe Combined Immunodeficiency/genetics , Adult , Amino Acid Substitution , Antigen Presentation , Chemotaxis, Leukocyte , Golgi Apparatus/chemistry , Humans , Immunogenicity, Vaccine , Inducible T-Cell Co-Stimulator Ligand/chemistry , Inducible T-Cell Co-Stimulator Ligand/genetics , Inducible T-Cell Co-Stimulator Ligand/immunology , Inducible T-Cell Co-Stimulator Protein/immunology , Infections/etiology , Lymphocyte Activation , Male , Mutation, Missense , Phenotype , Protein Transport , Recurrence , Severe Combined Immunodeficiency/immunology , T-Lymphocytes/immunologyABSTRACT
Human inducible co-stimulator ligand (GL50, CD275), also known as B7-H2 or ICOSL, is a positive co-stimulatory molecule of B7/CD28 superfamily, which plays a critical role in immune response. Here we generated two novel mouse anti-human GL50 monoclonal antibodies (MAbs) using classical hybridoma technology. The two MAbs (clones 2B4 and 4D11) were IgG1 (κ) and IgG2a (κ), respectively, and bound specifically to human GL50. Epitope competition assay showed that 2B4 and 4D11 bind to the same epitope of GL50, which is not recognized by the commercially available GL50 MAb (9F-8A4). Functionally, the two MAbs act as a blocker of T cell proliferation. Taken together, as useful tools, these two antibodies might be of great value for further exploration of the immune identification and function of GL50.